1. Field of the Invention
The present invention pertains to magnetic disk storage apparatus, and more particularly, it pertains to the high capacity hard disk drive modules having a rotatable stack of closely spaced disks with multiple magnetic head tranducer arms movable radially of the stack for reading from and recording on opposite faces of each of the disks.
2. Description of the Prior Art
In today's markets, with the proliferation of the use of computers, both for personal and for business use, there is an ever increasing demand for higher and higher capacity memory devices. The basic memory storage device of computers is the so-called hard disk drive comprised of a rigid disk, or more typically, a stack of closely spaced rigid disks, with actuator arms carrying tiny magnetic transducer heads being adapted to move radially within such stack of disks in comb-like fashion to record and read magnetically encoded data along circumferential cracks on both faces of all of such superimposed disks. Since computers are built with certain predefined spaces for accommodating the aforedescribed hard disk drive devices, the overall dimensions of such devices, or modules, have been fixed into a plurality of package sizes or form factors. Thus, increases in the memory capacity of a disk drive module of a given industry standard package size have been made either by increasing the density of the data written on a given area of a disk or by an improved mechanical design, e.g., by providing a greater number of disks in a given package size.
In addition to maximizing the number of disks in a given package size, various attempts have been made to improve the magnetic head positioning mechanisms, i.e., the actuator arms and the drive arrangements thereof, in order to improve access time, positioning precision, and reading reliability. In prior art mechanisms, two different types of magnetic head positioner mechanisms, or actuator arms, have been developed. Linear positioners comprise a carriage carrying actuator arms which are moved radially with respect to the axis of rotation of the disks in order to position the magnetic heads along various of the circumferentially arranged tracks. Pivotally mounted actuator arms, or rotational positioners, pivot about an axis parallel to the axis of the disk stack so that the magnetic heads carried at the distal ends thereof are swung in arcuate paths across the magnetically encoded tracks of the disks.
Such pivotally mounted actuator arm assemblies generally include counterbalancing drive arms provided with a voice-coil motor or servo-motor for providing the rotational movement thereto. There has been a continuing search for new and different ways to design such rotational drive mechanisms in order to improve data access time and reading reliability, and various arrangements have been proposed in order to fit within the predescribed package size dimensions and yet provide as efficient and reliable a mechanism as possible.
In a conventional actuator arm assembly of the typical prior art hard disk drive devices the actuator arms and the magnetic heads supported thereby are positioned one above the other in a superimposed arrangement so that all of the arms move jointly within the disk stack with the magnetic heads traversing identical superimposed paths across the opposed faces of the disks. This requires that the spacing between adjacent disks be such as to accommodate a pair of magnetic heads, the flexure mountings therefor, and the required supporting arm dimensions. In recent years, attempts have been made to decrease this required dimension between disks in a stack by offsetting the magnetic heads and their flexure mountings between the opposed faces of adjacent disks so that the spacing between disks can be reduced to accommodate just slightly greater than that required for the support arm and a single flexure mounting and its supported magnetic head. For example, in U.S. Pat. No. 4,800,455 to Takizawa, a linear positioning mechanism is shown wherein the magnetic head support arms for moving radially between a pair of opposed disk faces are offset and arranged at an angle to each other: thus, the required spacing between disks is just slightly more than that required for a single support arm, and offset, but identical, radial paths of movement are provided across the opposed faces of the disks by the actuator arms.
A rotational magnetic head positioning mechanism having a similar disk spacing minimization concept is shown in U.S. Pat. No. 4,937,693 to Connolly et al. In the disk drive structure shown and described in this patent, a pair of magnetic heads and their supporting flexure arms are mounted in parallel upon a pivotally mounted actuator arm and are adapted to be swung through slightly offset arcuate paths between adjacent disks of the disk stack. Such paths, however, will not be identical and will vary in length whereby the magnetic heads when starting at the same track position (the outermost concentric track on the disks) will finish at different track positions as they are moved simultaneously across the respective faces of the opposed disks. Thus, one of the heads will not fully utilize the tracking space on its disk. Furthermore, the differences in the skew angles of the head gaps of the heads with the tracks on the disks creates tracking problems which can effect the reliability of the system.
A similar rotary actuator structure for a stacked magnetic disk arrangement is shown in U.S. Pat. No. 5,027,242 to Nishida et al. Again, a pair of magnetic transducer heads are located on a pair of flexure arms mounted in generally parallel relationship on a common actuator arm. The magnetic heads and their supporting flexure arms are moved in arcuate paths across the opposed faces of a pair of opposed disks in a disk stack. In the arrangement shown and described in the patent, the problem of the apparatus of the aforedescribed U.S. Pat. No. 4,937,693 are magnified in that the tracking paths of the adjacent magnetic heads vary significantly as the magnetic heads are moved radially inwardly across the opposed disk faces so that the inner head passes across a significantly fewer number of the circumferentially arranged tracks. Furthermore, the difference in the paths of movement of the heads of necessity creates significant problems in maintaining acceptable skew angles of the head gaps with the recording tracks on the disk throughout the radial movement of the heads.
Multiple magnetic heads can also be used on a single actuator arm communicating with a single surface of a magnetic recording disk to reduce data access time. As shown, for example, in U.S. Pat. No. 4,787,001 to Okutsu, a rotary actuator arm mounts a pair of magnetic heads one of which is adapted to move over the radially outer portion of the recording tracks on the disk while the other head moves across the radially inner tracks on the disk.